Is the 6.6 gas engine Flex Fuel?

Gagliano7 · August 21, 2019

I have been searching and i haven't seen if the new 6.6 is flex fuel. Anyone know for sure. Thanks

Booger T · August 21, 2019

Mine is not. Don't know if they are all that way or not.

ShotgunZ71 · August 21, 2019

No, the new 6.6L gas engine is not flex fuel. E15 max for that one.

Gagliano7 · August 22, 2019

Ok thanks. I am surprised that got rid of the flex fuel.

Gagliano7 · August 22, 2019

On 8/21/2019 at 6:54 AM, Booger T said:

Mine is not. Don't know if they are all that way or not.

What kind of mileage are you getting with the 6.6?

ApertureX · August 22, 2019

9 minutes ago, Gagliano7 said:

Ok thanks. I am surprised that got rid of the flex fuel.

The GM engineer that I saw interviewed said that it "currently" is not flex fuel. They will most likely make a flex version in the future, but right now with a new design they opted to just make sure it ran as designed on 87 gas first.

Give it a few years and there will probably be a conversion kit available in the aftermarket once the production engine is E85 capable.

Booger T · August 22, 2019

24 minutes ago, Gagliano7 said:

What kind of mileage are you getting with the 6.6?

While I don't drive it much (it's my wife's truck) what little I have drove it is showing 16-17 highway and around 13 in town and short trips. Slightly better than the 6.0 that she did have. Only have 500 miles on it currently so hoping it may improve some.

shreff86 · August 27, 2019

On 8/22/2019 at 9:31 AM, Booger T said:

While I don't drive it much (it's my wife's truck) what little I have drove it is showing 16-17 highway and around 13 in town and short trips. Slightly better than the 6.0 that she did have. Only have 500 miles on it currently so hoping it may improve some.

What year was your 6.0 and gear did it have? What were you mpg with it in similar situations? Thanks

Booger T · August 27, 2019

The 6.0 was and 07 and had 3.73 gears. It would generally get around 15-16 on the highway and and maybe 12 around town on a good day.

Jeff.Cole · March 24, 2021

in 2021 Flex Fuel is available in a work truck model for $100

Edited March 24, 2021 by Jeff.Cole

MTU Alum · March 24, 2021

49 minutes ago, Jeff.Cole said:

in 2021 Flex Fuel is available in a work truck model for $100

Available in work truck trim only. I drove one for about four months on e85. I got around 11 combined mpg vs 13.5 on e10.

#iworkforGM

Jeff.Cole · March 29, 2021

I can get e-85 for about a dollar less per gallon compared to E-10 delivered to my farm. Thats about $0.15 for E-85 per mile and $0.20 per mile for E-10 Giving E-85 a saving currently of 25% over E-10 and valuing E-10 at 2.69/Gal.

nards444 · March 29, 2021

3 hours ago, Jeff.Cole said:

I can get e-85 for about a dollar less per gallon compared to E-10 delivered to my farm. Thats about $0.15 for E-85 per mile and $0.20 per mile for E-10 Giving E-85 a saving currently of 25% over E-10 and valuing E-10 at 2.69/Gal.

Havent seen numbers for this engine. Typically E-85 means 20-25% less efficient fuel economy. I know some parts of the country the math works out still, and E-85 actually provides better performance as well. But around here if you can find it, its not worth buying

newdude · March 29, 2021

Although there doesn't seem to be an SAE rated dyno graph for it, the 5.3 had one for the L83 variant 2014-2018. GM had a published 25hp gain (355hp 87 octane vs. 383hp E85) and a 33 ft.lbs torque gain (383 ft.lbs 87 octane vs. 416 ft.lbs E85).

One could perhaps assume that this would follow suit +/- a couple HP on the 6.6. Someone would ideally have to dyno a WT trim HD equipped with the factory flex fuel option to verify.

DI engines pick up good #s on it. The old port fuel LS engines gained 5-7hp and 12-14 ft.lbs torque on factory flex trucks SAE rated.

Edited March 29, 2021 by newdude